Means for measuring the liquid level in a reservoir for a fuel cell

ABSTRACT

A small fuel cell ( 10 ) powers a portable electronic device ( 12 ) and contains a fuel reservoir ( 14 ) and a device ( 16 ) that measures the amount of liquid fuel ( 18 ) that is in the reservoir. The fuel cell operates on hydrogen that is obtained from a liquid hydrocarbon fuel, such as alcohol or other hydrocarbons. The liquid fuel is typically converted into hydrogen by a reforming process. The reservoir that is connected to the fuel cell has an indicia ( 19 ) that is readable by a human user of the portable electronic device, for measuring the amount of liquid hydrocarbon fuel that is present in the reservoir. Typically, the indicia consist of a sight glass, a capacitive element, a resistive element, a transparent portion of the reservoir, a float, or an acoustic transmitter coupled with an acoustic receiver.

TECHNICAL FIELD

[0001] The present invention is related to systems for measuring andindicating the level and/or quantity of liquid fuel in a container orstorage tank of a fuel cell.

BACKGROUND

[0002] In recent years, nearly all electronic devices have been reducedin size and made lightweight, in particular portable electronic devicessuch as cellular telephones, two-way radios, laptop computers, personaldigital assistants (PDAs), etc. This advancement has been made possible,in part, by the development of new battery chemistries such asnickel-metal hydride, lithium ion, zinc-air, and lithium polymer thatenable larger amounts of power to be packaged in a smaller container.These secondary or rechargeable batteries need to be recharged upondepletion of their electrical capacity. This is typically performed byconnecting the battery to a battery charger that converts alternatingcurrent to a low level direct current of 2-12 volts. The charging cycletypically lasts a minimum of 1-2 hours, and more commonly 4-14 hours.Although the new batteries are a tremendous advancement over theprevious generations of batteries, they still suffer from the need forsophisticated charging regimens and the slow charging rates. Some havesought to replace electrolytic batteries with fuel cells. Simply put,fuel cells catalyticly convert a hydrogen molecule to hydrogen ions andelectrons, and then extract the electrons through a membrane aselectrical power, while oxidizing the hydrogen ions to H₂O andextracting the byproduct water. The tremendous advantage of fuel cellsis the potential ability to provide significantly larger amounts ofpower in a small package, as compared to a battery. However, the problemof how to replenish the supply of hydrogen fuel to the spent fuel cellstill seeks an elegant and practical solution before widespread consumeracceptance occurs. Some have sought to use methanol as the source ofhydrogen, by catalyticly converting or ‘reforming’ the methanol usingexotic schemes or in the direct methanol fuel cell. Methanol is moreattractive to consumers than gaseous hydrogen, as it is more readilyavailable and can be more easily stored and contained. However, themethanol still needs to be replenished from time to time, and it wouldbe desirable if the user of a small methanol-powered fuel cell couldeasily and readily determine how much longer the fuel cell will operateuntil the fuel supply is exhausted. In other words, to measure how muchliquid methanol remains in the storage container.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The sole drawing FIGURE is an isometric drawing of an electronicdevice powered by a fuel cell having visually readable indicia inaccordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0004] While the specification concludes with claims defining thefeatures of the invention that are regarded as novel, it is believedthat the invention will be better understood from a consideration of thefollowing description in conjunction with the drawing figures, in whichlike reference numerals are carried forward. Referring now to thedrawing FIGURE, a small fuel cell 10 that can be used to power aportable electronic device 12 has incorporated therewith a fuelreservoir 14 that has a means for measuring 16 the amount of liquid fuel18 that is in the reservoir. The fuel cell operates on hydrogen that isobtained from a liquid hydrocarbon fuel, such as alcohol or otherhydrocarbons. The liquid fuel is typically converted into hydrogen by areforming process. The reservoir that is connected to the fuel cell hasan indicia 19 that is readable by a human user of the portableelectronic device, for measuring the amount of liquid hydrocarbon fuelthat is present in the reservoir. Typically, the indicia 19 consist of asight glass, a capacitive element, a resistive element, a transparentportion of the reservoir, a float, or an acoustic transmitter coupledwith an acoustic receiver. In an alternate embodiment, the level ofliquid fuel in the fuel cell is communicated to the user of theelectronic device by a display 20, such as a liquid crystal display(LCD) or a series of light emitting diodes (LED) that are appropriatelyconnected to a sensor on or in the reservoir. The display 20 can beconveniently located on either the electronic device or on the fuel cellor on the fuel cell reservoir.

[0005] Many techniques have been developed to measure the liquid levelsand liquid quantities in storage tanks. One system for measuring thefuel level in the fuel tank of a motor vehicle employs a variableresistor within the tank. The wiper arm of the variable resistor isconnected through a pivot to a float which monitors the upper level ofthe fuel in the tank. Other systems use immersion capacitor units orprobes in liquid containers or tanks in combination with suitableelectrical circuitry and measuring and indicating instrumentation, wherethe liquid itself forms the dielectric between the plates. Thecapacitive value of the immersion capacitor is variable and changes withrespect to the level of liquid in the container. By constructing thecapacitor unit of multiple pairs of plates which are placed in differentareas of the container, the effects of liquid sloshing or surging andliquid level shift are reduced, so as to obtain an accurate capacitancevalue for the immersion unit. The immersion capacitor unit (whether ofsingle pair or multiple pair plate design) is electrically connectedinto a bridge circuit having two condensers of fixed and equal capacity,each forming an arm of the bridge, the remaining two arms of the bridgebeing made up of a variable capacitor and the immersion capacitor. Thebridge circuit (of well known Wheatstone configuration) is connected toa source of alternating current of predetermined frequency and detectorand measurement indicating circuitry. The bridge circuitry is arrangedto be in an unbalanced state so long as any liquid remains in thecontainer in the dielectric space between the plates of the immersioncapacitor unit.

[0006] In U.S. Pat. No. 4,194,395 granted to T. J. Wood, entitled“Capacitive Liquid Level Sensor,” a capacitive type sensor for measuringliquid levels has a plurality of like plate-type capacitors arranged inparallel. The dielectric spaces of each capacitor (isolated from eachother) receive the liquid to be measured which (with air, if any, abovethe liquid) establishes the dielectric for the spaces and thus thecapacitance value of each capacitor. Since the capacitors areidentically configured they exhibit equal values of capacitance onlywhen the liquid dielectric (and air, if any) between the plates of eachcapacitor covers equal areas. When the liquid within a container isbeing measured as to its height level or volume and is sloshing or hasits level disoriented with respect to its normal liquid level referenceplane, the liquid (functioning as a dielectric) covers different areasof the capacitors and they exhibit dissimilar values of capacitance.Associated circuitry interrogates the capacitors and at points when thecapacitance values approach equality the system reads one of the valuesand registers the liquid level or quantity of liquid remaining in thecontainer. These types of systems overcome the problems of fuel levelshift, sloshing, or orientation of the reservoir while measuring theamount of liquid in the reservoir or tank.

[0007] Another embodiment of the invention utilizes a sight glass tovisually determine the amount of fuel in the reservoir. As depicted inFIG. 1, the reservoir 14 can have the sight glass 16 incorporated as anintegral part of the container, i.e. as a transparent portion of thecontainer 14. This can be accomplished, for example, by making thereservoir 14 from plastic and making the sight glass 16 from clearplastic. The user then looks at the sight glass and corresponds thelevel of fuel to a scale or indicia 19 that is part of the sight glassor is inscribed on the reservoir. Another visual technique finds theentire fuel reservoir made of a transparent or translucent material soas to make the fuel level easily seen from any angle. A colorant can beoptionally added to the fuel in any of the visual techniques to assistin determining the fuel level.

[0008] Still another embodiment measures the level of fuel in thereservoir by measuring an electrical resistance through the fuel in thereservoir. This is accomplished via conductive elements placed atopposing ends of the reservoir. The conductive elements are used tomeasure the resistance across the fuel, whereby higher levels of fuelwould result in lower resistance readings. The resistance readings arethen cross referenced to a lookup table which provides the correspondingfuel level, which is communicated to the user via a display, speechmessage, light emitting diode gauge, or other common means.

[0009] A further embodiment of the invention utilizes acoustic signals.The signals are transmitted in the fuel reservoir, the signals aredetected by a detector appropriately located in the reservoir, aresponse is measured by the detector, the measurement is compared to alookup table, and a corresponding fuel level is determined andcommunicated to the user via a display, speech message, light emittingdiode gauge, or other common means. Alternatively, a speaker can be usedto generate a sine wave signal while the electrical resistance of thespeaker coil is measured. Depending on the level of fuel in thereservoir and the corresponding air space above the fuel, the forcerequired by the speaker to move the air in the space above the fuelwould result in a given electrical resistance and hence the fuel levelcan be determined. Yet another embodiment of the acoustic measuringmethod bounces an acoustic signal off the top surface of the fuel tomeasure the fuel level by determining the distance from the top of thecontainer to the fuel surface. The distance can be measured bycalculating the time delay between the transmission of the signal fromthe top of the reservoir towards the fuel surface and receipt of thereflected signal back at the top of the reservoir.

[0010] While the preferred embodiments of the invention have beenillustrated and described, it will be clear that the invention is not solimited. Numerous modifications, changes, variations, substitutions andequivalents will occur to those skilled in the art without departingfrom the spirit and scope of the present invention as defined by theappended claims. For example, an additional liquid level measuringmeans, similar to those espoused above, can be incorporated and used tomeasure the amount of water in a second reservoir, when water is held inthe second reservoir and used to dilute the methanol.

What is claimed is:
 1. A fuel cell system for a portable electronicdevice, comprising: a fuel cell capable of operating on hydrogen that isobtained from methanol; a reservoir for storing a supply of methanol,suitably connected to the fuel cell; and the reservoir furthercomprising a fuel quantity measuring means.
 2. The fuel cell asdescribed in claim 1, wherein the fuel quantity measuring meanscomprises a sight glass.
 3. The fuel cell as described in claim 1,wherein the fuel quantity measuring means comprises a float.
 4. The fuelcell as described in claim 1, wherein the fuel quantity measuring meanscomprises a transparent reservoir.
 5. The fuel cell as described inclaim 1, wherein the fuel quantity measuring means comprises a resistiveelement.
 6. The fuel cell as described in claim 1, wherein the fuelquantity measuring means comprises a capacitive element.
 7. The fuelcell as described in claim 1, wherein the fuel quantity measuring meanscomprises an acoustic transmitter and an acoustic receiver.
 8. A fuelcell system for a portable electronic device, comprising: a fuel cellthat operates on hydrogen obtained from a liquid hydrocarbon fuel; areservoir for containing a supply of the liquid hydrocarbon fuel, saidreservoir connected to the fuel cell; and the reservoir furthercomprising an indicia readable by a human user of the portableelectronic device, for measuring the amount of liquid hydrocarbon fuelthat is present in the reservoir.
 9. The fuel cell as described in claim8, wherein the indicia comprises a sight glass.
 10. The fuel cell asdescribed in claim 8, wherein the indicia comprises a float.
 11. Thefuel cell as described in claim 8, wherein the indicia comprises atransparent reservoir.
 12. The fuel cell as described in claim 8,wherein the indicia further comprises a sensing means.
 13. The fuel cellas described in claim 12, wherein the sensing means comprises aresistive element.
 14. The fuel cell as described in claim 12, whereinthe sensing means comprises a capacitive element.
 15. The fuel cell asdescribed in claim 12, wherein the sensing means comprises an acoustictransmitter and an acoustic receiver.
 16. The fuel cell system asdescribed in claim 8, wherein the indicia comprises a liquid crystaldisplay.
 17. A fuel cell system for powering a portable electronicdevice, comprising: a portable electronic device having a radiotransmitter and a radio receiver; a fuel cell electrically andmechanically coupled to said portable electronic device, said fuel cellcapable of operating on hydrogen that is obtained from methanol; areservoir for storing a supply of methanol, suitably connected to thefuel cell; and the reservoir further comprising a fuel quantitymeasuring means.
 18. The fuel cell system as described in claim 17,wherein the fuel quantity measuring means comprises a liquid crystaldisplay in the portable electronic device.
 19. The fuel cell system asdescribed in claim 17, wherein the fuel quantity measuring meanscomprises a liquid crystal display disposed on the fuel cell.